CBA Center for Backyard Astrophysics



Hump Zoology in CVs

as seen by CBA zookeepers

taken from:
Appendix A, The 2001 Superoutburst of WZ Sagittae

[nicely-formatted version of this table (PDF)]

in this HTML version of the table below,
w is equivalent to the lower-case Greek omega;
W to the upper-case Greek omega

1. Orbital Hump · 2. Outburst Orbital Hump · 3. Common Superhump
4. Late Superhump · 5. Positive Superhump · 6. Apsidal Superhump
7. Negative Superhump · 8. Nodal Superhump · 9. Permanent Superhump
10. Quiescent Superhump · 11. Superhumper · Notes


Type:   1. Orbital Hump
Meaning: Signal at the orbital frequency wo in quiescence.
Example Stars: U Gem, WZ Sge
Alleged Origin: Presentation effect of hot spot (stream-disk impact region).

Type:   2. Outburst Orbital Hump
Meaning: Signal at or very near wo in outburst. Quite rare; appears to be transiently present in a few SU UMa stars (possibly restricted to the WZ Sge class) in the earliest stage of outburst. Sometimes also called early, immature, and orbital superhumps; but we prefer to restrict "superhump" to cases where the frequency is distinct from wo.
Example Stars: WZ Sge, AL Com
Alleged Origin: Unknown.

Type:   3. Common Superhump
Meaning: Signal at wo-W, shown by all SU UMa stars in outburst; decays roughly on a timescale of 1-3 weeks. Often of very large amplitude (0.4 mag), and thus a major element in the outburst energy budget. So universal and so extensively studied that "superhump", sans qualifier, often implies a common superhump.
Example Stars: SU UMa, VW Hyi, 54 others
Alleged Origin: Periodic tidal disturbance of the disk by the orbiting secondary (thus requiring a slow apsidal advance to match the frequency shift to wo-W).

Type:   4. Late Superhump
Meaning: Signal at wo-W, sometimes following (3) and basically defined by a sudden phase shift in (3) of ~0.5 cycles, with little or no change in period.
Example Stars: OY Car, VY Hyi
Alleged Origin: Not securely known, but definitely similar to (3) - features apsidal advance of an "elliptical" disk.

Type:   5. Positive Superhump
Meaning: A general term for any signal with P slightly exceeding Po (a small positive increment in period) and hence w=wo-W. Includes all common superhumps.
Example Stars: 77 CVs
Alleged Origin: Just an observational term.

Type:   6. Apsidal Superhump
Meaning: Alternate to (5), if you subscribe to the theory that (5) arises from apsidal advance ("precession") of the disk, in which case W is the precession frequency. Includes all common superhumps, if you buy that theory.
Example Stars: 77 CVs, probably
Alleged Origin: Probably the same as (3) or (4).

Type:   7. Negative Superhump
Meaning: A general term for any signal with P slightly less than Po (a small negative increment in period) and hence w=wo+N.
Example Stars: V503 Cyg, TV Col, V603 Aql
Alleged Origin: Just an observational term.

Type:   8. Nodal Superhump
Meaning: Alternate to (7), if you subscribe to the theory that (7) arises from nodal precession (wobble) of the disk, in which case N is the precession frequency.
Example Stars: same, probably
Alleged Origin: Not securely known.

Type:   9. Permanent Superhump
Meaning: Any positive or negative superhump which is long-lived (months or longer) and not associated with eruption.
Example Stars: AM CVn, V603 Aql, BK Lyn
Alleged Origin: Probably same as (3), (4), and (8).

Type: 10. Quiescent Superhump
Meaning: Extremely rare, and not a term in general use. A superhump in states of very low luminosity, with no connection yet established to the other superhump types.
Example Stars: AL Com, CP Eri
Alleged Origin: Unknown.

Type: 11. Superhumper
Meaning: A star which engages in superhumps.

         Notes

(a)  "Outburst" here means superoutburst. Happily, we still know of no related periodic signals characteristic of normal outburst.

(b)  It may well be true that all apsidal precession is prograde (giving a positive superhump) and all nodal precession is retrograde (giving a negative superhump). The limited data available now are consistent with this. If counterexamples are found, these definitions would be affected somewhat.

(c)  Superhumps can be characterized by 3 fundamental frequencies (wo, W, N), and the dominant signal is nearly always wo-W or wo+N. But studies of high sensitivity and frequency resolution often reveal components with w=nwo-mW (where n=any small integer and m=1, 2, ..., n) or nwo+N (same terminology). We consider these as "fine structure" and thus outside this classification effort.